By developing information communication, such as the Internet, it becomes easy for a plurality of persons each belonging to different organizations to do business in cooperation with each other. For example, assume that a company A possesses customer data and a company B possesses know-how of data analysis. In this case, company A often requests company B to analyze the customer data by supplying the customer data in a database through the Internet. Company A receives an analysis report of the customer data from company B, and sends an indication of the analysis again to company B using E-mail. Briefly, by giving and taking of various kinds of electronic documents through the Internet, business can be easily executed among a plurality of companies (organizations).
In transfer (giving and taking) of electronic documents among different companies, management of important information such as customer data or company secret data in the electronic document is a question. In the above example of the database supplied from the company A to the company B, secret data not to become known by the company B is often included. In the prior art, secret data is deleted by a user himself or by a computer program, or ciphered as meaningless data for person. However, if deleted (or ciphered) data includes information necessary for analysis, the information cannot be utilized for analysis. Furthermore, if the secret data is ciphered as a character-string that prevents a person from understanding, a hindrance often occurs in the business between the company A and the company B.
In data communication through the Internet, a prior method for hiding secret data for a sender, Japanese Patent Disclosure (Kokai) PH2000-324094 is known. In this method, personal information such as a name is hidden in the sending information. However, other kinds of secret data (all contents) in the electronic document cannot be hidden. Furthermore, the hidden part (anonymous part) in the electronic document cannot be returned to a real name.
As mentioned-above, when the electronic document including important information of the user's own company is transferred and analyzed by another company, the other company is in need of information about the important information. However, in the prior method in which secret data is deleted or ciphered, it is a problem that a document processing person (analyst) in another company cannot understand the electronic document sufficiently for analysis.